Photometric apparatus for camera

ABSTRACT

A photometric apparatus which satisfies the demands for reductions in the size, thickness and cost and which is highly optioned despite a simple arrangement. A photometric optical system provided separately from a photographic optical system ( 1 ) has at least one diffractive optical element ( 10 ). The diffraction surface of the diffractive optical element ( 10 ) is provided on a convex lens surface to have a converging action. Alternatively, the diffraction surface of the diffractive optical element ( 10 ) is provided on a concave lens surface to have a diverging action.

This is a division of application Ser. No. 08/863,005, filed May 23,1997, now U.S. Pat. No. 6,072,959.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a photometric apparatus for a camera.More particularly, the present invention relates to a photometricapparatus for a camera which uses a diffractive optical element.

2. Discussion of Related Art

A conventional photometric apparatus for a single-lens reflex camera,for example, is arranged as shown in FIG. 23. A conventional photometricapparatus for a lens shutter camera is arranged as shown in FIG. 24. Inthese figures, reference numeral 1 denotes a photographic opticalsystem; 2 denotes a finder optical system; 3 denotes a condenser lensfor photometry; 4 denotes a light-receiving element for photometry; 5denotes a quick return mirror; 6 denotes a sub-mirror; 7 denotes a filmplane; 8 denotes a photometer window; and 9 denotes a finder window. Inmany cases, the condenser lens 3 consists essentially of a single lenselement by virtue of the spread of aspherical plastic lenses and othersimilar lenses. This contributes to reductions in the size, thicknessand cost of photometric apparatuses.

In recent years, however, there have been increasing demands forreductions in the size, thickness and cost of cameras and forachievement of higher value-added cameras. Under these circumstances,photometric apparatuses must be designed to be capable of meeting thesedemands.

Recently, the use of diffractive optical elements (hereinafter referredto as “DOE”) has begun in consequence of the improvement in opticaltechnology. Examples of prior art that use a DOE in a photometricapparatus for a camera include Japanese Patent Application UnexaminedPublication Numbers [hereinafter referred to as “JP(A)”]5-27304 and6-250251.

JP(A) 5-27304 proposes a photometric system in which a bundle of lightrays is diffracted and reflected by using a hologram, and a part of theray bundle is separated by a half-mirror and used for photometry.

JP(A) 6-250251 proposes a photometric apparatus for a lens shuttercamera in which a DOE is set in front of an aperture stop in aphotographic optical system to divide an optical path for photometry.

In particular, lens shutter cameras need to make various improvements interms of the size of the apparatus, the restriction on design due to thepresence of the photometer window, the reliability in the accuracy ofphotometry, the production cost, etc.

In a case where the condenser lens is formed from a single lens elementas has been stated above, the radius of curvature of the condenser lensis reduced in order to ensure an extremely strong power, and the centerthickness of the lens is increased in order to ensure the requiredthickness for the lens edge, causing the apparatus to increase inoverall thickness. This has a significant effect on the layout of theinterior of the camera and leads to an increase in the overall size ofthe camera.

The same is said of the presence of the photometer window. In addition,the photometer window restricts the design freedom.

It is conceivable for the optical axis to be bent to make good use ofthe limited space. However, the provision of a reflecting member or thelike leads to a rise in the cost, unfavorably.

Further, parallax may occur because of the external photometry type, andit is difficult to perform photometry according to photographicconditions (e.g. field angle changes during zooming photography orswitching between normal and panoramic photography modes). Therefore, itis difficult to obtain high reliability.

In the case of a thick and long lens barrel, as in recent zoom lenses ofhigh zoom ratio, the lens barrel itself may vignette a part of theacceptance angle.

Single-lens reflex cameras are also demanded to be further reduced insize, weight and cost. Some single-lens reflex cameras employ in-finderphotometry. In this case, however, the amount of light reaching the filmplane and the amount of light reaching the light-receiving element donot coincide with each other. Therefore, the photometry accuracy isunfavorably low.

There are apparatuses that use a Fresnel lens. However, this type ofapparatus is not efficient because it suffers from a large loss of lightquantity.

SUMMARY OF THE INVENTION

In view of the above-described problems associated with the prior art,an object of the present invention is to provide a photometric apparatuswhich satisfies the demands for reductions in the size, thickness andcost and which is highly optioned despite a simple arrangement bydisposing a DOE even more effectively in the above-described photometricapparatus according to the prior art.

To attain the above-described object, the present invention provides aphotometric apparatus for a camera, which is characterized in that aphotometric optical system provided separately from a photographicoptical system has at least one diffractive optical element.

In addition, the present invention provides a photometric apparatus fora camera, which is characterized in that an exterior part of the camerais formed from a diffractive optical element, and a bundle of light rayspassing through the diffractive optical element is led to alight-receiving element for photometry.

In addition, the present invention provides a photometric apparatus fora single-lens reflex camera, which is characterized in that aphotometric optical system includes a half-mirror or a reflecting mirrorwhich is provided with a diffraction surface having a converging action,and at least a part of a bundle of light rays passing through orreflected by the diffraction surface is led to a light-receiving elementfor photometry.

In addition, the present invention provides a photometric apparatus fora camera, which is characterized in that at least one diffractionsurface having an optical path dividing action is provided on a lenssurface of a photographic optical system in an area where an effectiveray bundle passes, and at least a part of a bundle of light rays passingthrough the diffraction surface is led to a light-receiving element forphotometry, and that the diffraction surface has concentric rotationallysymmetric patterns formed thereon.

In addition, the present invention provides a photometric apparatus fora camera, which is characterized in that at least one diffractionsurface is provided on an external portion of an optical system otherthan a photometric optical system in an area other than an area where aneffective ray bundle passes, and a bundle of light rays passing throughthe diffraction surface is led to a light-receiving element forphotometry.

In addition, the present invention provides a photometric apparatus fora camera, which is characterized in that at least two diffractionsurfaces are provided on the same substrate, and that a bundle of lightrays passing through at least one of the diffraction surfaces is led toa light-receiving element for distance measurement, and a bundle oflight rays passing through at least one other of the diffractionsurfaces is led to a light-receiving element for photometry.

In addition, the present invention provides a photometric apparatus fora camera, which is characterized in that a photometric optical systemhaving at least one diffractive-optical element with at least onediffraction surface is adapted to change a magnification according tophotography conditions such as a magnification change and switching to apanoramic photography mode, and a bundle of light rays subjected to amagnification change by the photometric optical system is led to alight-receiving element for photometry.

According to the present invention, a diffractive optical element isprovided in a photometric optical system for a camera, thereby making itpossible to provide a photometric apparatus for a camera which satisfiesthe demands for reductions in the size, thickness and cost of theapparatus. Further, the present invention enables the photometricapparatus to be highly optioned despite a simple arrangement whilesatisfying the demands for reductions in the size, thickness and cost.

Still other objects and advantages of the invention will in part beobvious and will in part be apparent from the specification.

The invention accordingly comprises the features of construction,combinations of elements, and arrangement of parts which will beexemplified in the construction hereinafter set forth, and the scope ofthe invention will be indicated in the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a conceptual view showing a first embodiment of the presentinvention.

FIG. 2 is a conceptual view showing a second embodiment of the presentinvention.

FIG. 3 is a conceptual view showing a third embodiment of the presentinvention.

FIG. 4 is a conceptual view showing a fourth embodiment of the presentinvention.

FIG. 5 is a conceptual view showing a fifth embodiment of the presentinvention.

FIG. 6 is a conceptual view showing a sixth embodiment of the presentinvention.

FIG. 7 is a conceptual view showing a seventh embodiment of the presentinvention.

FIG. 8 is a conceptual view showing an eighth embodiment of the presentinvention.

FIG. 9 is a conceptual view showing a ninth embodiment of the presentinvention.

FIG. 10 is a conceptual view showing a tenth embodiment of the presentinvention.

FIG. 11 is a conceptual view showing an eleventh embodiment of thepresent invention.

FIG. 12 is a conceptual view showing a twelfth embodiment of the presentinvention.

FIGS. 13(a), 13(b) and 13(c) show patterns on diffraction surfaces inthe twelfth and thirteenth embodiments of the present invention.

FIG. 14 is a conceptual view showing the thirteenth embodiment of thepresent invention.

FIG. 15 is a conceptual view showing a fourteenth embodiment of thepresent invention.

FIGS. 16(a) and 16(b) are conceptual views showing a modification of thefourteenth embodiment.

FIG. 17 is a conceptual view showing a fifteenth embodiment of thepresent invention.

FIG. 18 is a conceptual view showing a sixteenth embodiment of thepresent invention.

FIG. 19(a) is a conceptual view showing a seventeenth embodiment of thepresent invention.

FIG. 19(b) shows patterns on a diffraction surface in the seventeenthembodiment.

FIG. 20 is a conceptual view showing an eighteenth embodiment of thepresent invention.

FIGS. 21(a) and 21(b) show patterns on a diffraction surface in anineteenth embodiment of the present invention.

FIG. 22 is a conceptual view showing a twentieth embodiment of thepresent invention.

FIG. 23 is a conceptual view showing a conventional photometric opticalsystem for a single-lens reflex camera.

FIG. 24 is a conceptual view showing a conventional photometric opticalsystem for a lens shutter camera.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The arrangement and operation of the photometric apparatus for a cameraaccording to the present invention will be described below by way ofembodiments.

FIGS. 1 to 5 show embodiments of a first photometric apparatus for acamera according to the present invention.

[First Embodiment]

FIG. 1 is a conceptual view showing a first embodiment of the presentinvention, in which a plate-shaped DOE 10 having a converging lensaction is provided in a photometric optical system for a single-lensreflex camera. A quick return mirror 5 having a half-mirror portion isdisposed in an optical path of a photographic optical system 1. A partof a bundle of light rays from the photographic optical system 1 passesthrough the half-mirror portion of the quick return mirror 5 and isreflected by a sub-mirror 6 and led through the DOE 10 to alight-receiving element 4 to perform photometry. In the firstembodiment, the DOE 10 has a converging lens action. In the firstembodiment, because the DOE 10 has a converging lens action, the lenssurface, which usually assumes a converging lens action, has anextremely gentle curvature. Consequently, the center thickness of thelens need not be increased to a considerable extent in order to ensurethe required thickness for the lens edge. Thus, the center thickness ofthe lens is favorably minimized.

In the first embodiment, the photometric optical system, which hasheretofore been formed from a single lens of large center thickness or aplurality of lenses of small center thickness, consists essentially of asingle thin DOE 10. Accordingly, it becomes possible to reduce thethickness of the photometric apparatus and to simplify the arrangementthereof. By forming the DOE 10 in the shape of a plate which is flat atboth sides thereof, an apparatus which is thinner and more lightweightcan be realized.

[Second Embodiment]

FIG. 2 is a conceptual view showing a second embodiment of the presentinvention, in which a plate-shaped DOE 10 having a converging lensaction is provided in a photometric optical system for a lens shuttercamera. A bundle of light rays entering the photometric optical systemthrough a photometer window 8 is led through the DOE 10 to alight-receiving element 4 to perform photometry. In the secondembodiment, the DOE 10 has a lens action as in the case of the firstembodiment. Thus, the second embodiment provides advantageous effectssimilar to those in the first embodiment.

In the second embodiment, the front surface of the DOE 10 is formed froma diffraction surface. The diffraction surface is provided on a curvedsurface having a positive (converging) lens action, and has a convergingaction. In the second embodiment, because the diffraction surface has aconverging action, the curvature of the curved surface provided with thediffraction surface is favorably gentle. In other words, the depth ofthe lens surface is shallow, and the external size (the overallthickness in the optical axis direction) of the lens is favorably small.Thus, it is possible to reduce the size and thickness of the apparatus.

In the second embodiment, the DOE 10 may be arranged such that the rearsurface of the DOE 10 is formed as a curved surface having a negative(diverging) lens action, and a diffraction surface having a divergingaction is provided on the curved surface. In this case, the DOE 10 has aconverging surface on the front side thereof and a diverging surface onthe rear side thereof. Consequently, it is possible to move the backprincipal point toward the front side and hence possible to reduce theoverall length of the photometric optical system. If the rear surface ofthe DOE 10 is also formed as a diffraction surface as in the case of thefirst embodiment, it becomes possible to reduce the thickness of theapparatus. More specifically, the rear surface of the DOE 10 can beformed with a gentle curvature while having a negative lens action.Accordingly, the depth of the lens surface becomes shallow, and theexternal size (the overall thickness in the optical axis direction) ofthe lens is reduced.

[Third Embodiment]

FIG. 3 is a conceptual view of a third embodiment of the presentinvention, in which the entrance and exit axes of a DOE 10 are notcoincident with each other. In the third embodiment, the center ofrotation of patterns constituting the DOE 10 is set off the opticalaxis, thereby allowing the DOE 10 to have an exit axis deflecting actionas well as a lens action. Thus, a light-receiving element 4 can bedisposed with a high degree of freedom, and it is possible to make gooduse of the limited space. The third embodiment also providesadvantageous effects similar to those in the first embodiment.

[Fourth Embodiment]

FIG. 4 is a conceptual view showing a fourth embodiment of the presentinvention in which a DOE and a light-receiving element 4 are integrallyformed as one unit. A package 11 covering the light-receiving element 4is provided with a diffraction surface 12 having a lens action.

[Fifth Embodiment]

FIG. 5 is a conceptual view showing a fifth embodiment of the presentinvention, in which a diffraction surface 12 having a lens action and alight-receiving element 4 are integrally formed on a prism.

In the fourth and fifth embodiments, the DOE is integrally formed withthe light-receiving element 4 for photometry, thereby enabling areduction in the number of components and simplifying the assembly ofthe apparatus. These embodiments also provide advantageous effectssimilar to those in the first embodiment.

In the above-described first photometric apparatus for a cameraaccording to the present invention, the provision of a DOE having a lensaction makes it possible to reduce the thickness of the photometricoptical system and to simplify the arrangement thereof.

Next, the arrangement and operation of a second photometric apparatusfor a camera according to the present invention will be described.

FIGS. 6 to 8 show embodiments of a second photometric apparatusaccording to the present invention. In all of these embodiments, adiffraction surface is provided in an exterior part (window) of acamera.

[Sixth Embodiment]

FIG. 6 is a conceptual view showing a sixth embodiment of the presentinvention. In this embodiment, the present invention is applied to aphotometric optical system for a lens shutter camera. A photometerwindow 8 is provided with a diffraction surface 12 having a converginglens action. A bundle of light rays entering the photometric opticalsystem through the photometer window 8 is led to a light-receivingelement 4 through a condenser lens 3 for photometry, thereby performingphotometry. In the sixth embodiment, the diffraction surface 12 is givena converging lens action to share the power required for the photometricoptical system with condenser lens 3. Thus, the condenser lens 3 can beformed from a surface having a gentle curvature, and the thickness ofthe optical system can be reduced.

If a diffraction surface 12 having a lens action of stronglight-gathering power is provided in the photometer window 8, it becomespossible to dispense with the condenser lens 3 and hence possible tofurther reduce the number of components and the size and cost of theapparatus.

[Seventh Embodiment]

FIG. 7 is a conceptual view showing a seventh embodiment of the presentinvention, in which a finder window 9 is formed integral with aphotometer window and provided with a diffraction surface 12 which isarranged such that the center of rotation of patterns thereof is set offthe optical axis. In this embodiment, the diffraction surface 12 has anexit axis deflecting action as well as a lens action of stronglight-gathering power. Thus, a light-receiving element 4 can be disposedwith a high degree of freedom, and it is possible to make good use ofthe space in the camera. Further, because the finder window 9 and thephotometer window are integral with each other, the number of componentsis reduced.

[Eighth Embodiment]

FIG. 8 is a conceptual view showing an eighth embodiment of the presentinvention, in which a diffraction surface 12 is provided in a waterproofcover window 13 of a photographic optical system 1, and a bundle oflight rays entering through the diffraction surface 12 is led to alight-receiving element 4. In this embodiment, the diffraction surface12 is given a lens action. Further, the diffraction surface 12 isprovided in the window 13 in front of the photographic optical system 1to solve the problem that a part of the acceptance angle may bevignetted by the lens barrel.

In the second photometric apparatus according to the present invention,a diffraction surface having a converging lens action is provided in anexterior part (window) of a camera. Thus, it becomes possible to reducethe thickness of the photometric optical system and to simplify thearrangement thereof. By giving a strong converging lens action to thediffraction surface, it becomes possible to reduce the number ofcomponents and to achieve a reduction in the cost.

In all the embodiments of the second photometric apparatus, thediffraction surface 12 is provided inside an exterior part (window) ofthe camera. The DOE is susceptible to dust, contamination, flaw, etc.Therefore, it is preferable to provide the diffraction surface inside anexterior part of the camera so that it will not be touched directly withthe user's hand.

Next, the arrangement and operation of a third photometric apparatusaccording to the present invention will be described.

FIGS. 9 and 10 show embodiments of the third photometric apparatusaccording to the present invention.

[Ninth Embodiment]

FIG. 9 is a conceptual view showing a ninth embodiment of the presentinvention. A diffraction surface 12 having both a converging lens actionand an exit axis deflecting action is provided on the back surface of aquick return mirror 5, which is a half-mirror incorporated in asingle-lens reflex camera. A bundle of light rays from a photographicoptical system 1 is incident on the quick return mirror 5. A part of theray bundle passes through the quick return mirror 5 and is bent by thediffraction surface 12 so as to be led to a light-receiving element 4 toperform photometry.

Conventionally, a photometric optical system for a single-lens reflexcamera is arranged as shown in FIG. 23 such that a bundle of light raysfrom a photographic optical system is incident on a quick return mirror5, and that part of the ray bundle which passes through the half-mirrorportion of the quick return mirror 5 is reflected by a sub-mirror 6located behind the quick return mirror 5 and thus led to alight-receiving element 4. In this embodiment, as shown in FIG. 9, thequick return mirror 5 is provided with the diffraction surface (DOE) 12to lead the ray bundle from the photographic optical system 1 directlyto the light-receiving element 4, thereby dispensing with the sub-mirrorthat has heretofore been provided, and thus realizing a cost reduction.The light-receiving element 4 can be installed at any position.Therefore, this embodiment is also advantageous to the layoutconfiguration. If the diffraction surface 12 is given a strongconverging lens action, it is possible to dispense with the condenserlens 3.

In the ninth embodiment, the diffraction surface 12 may be formed in amultiple structure consisting essentially of two diffraction surfaceshaving different exit angles so that a bundle of light rays passingthrough one diffraction surface is led to a light-receiving element forphotometry, and a bundle of light rays passing through the otherdiffraction surface is led to a light-receiving element for distancemeasurement. In this case, it becomes possible to perform distancemeasurement at the same time as photometry is performed. Accordingly,the number of components can be reduced. Thus, it is possible to achievea reduction in the cost and space savings.

[Tenth Embodiment]

FIG. 10 is a conceptual view showing a tenth embodiment of the presentinvention. The front side of a sub-mirror 6 located behind a quickreturn mirror 5 is provided with a diffraction surface 12 formed in amultiple structure consisting essentially of two diffraction surfaceshaving a converging lens action and blazed for each wavelength. A bundleof light rays reflected by the sub-mirror 6 is divided into two raybundles according to wavelengths. One ray bundle is led to alight-receiving element 4 for photometry, and the other ray bundle isled to a light-receiving element 14 for distance measurement.

In the tenth embodiment, it is possible to simultaneously performdistance measurement and photometry with the sub-mirror 6 disposed as inthe conventional apparatus. Accordingly, the number of components can bereduced. Thus, it is possible to achieve a reduction in the cost andspace savings.

By varying the light-gathering power for each blazed diffractionsurface, it becomes possible to arrange the components of thephotometric and distance measuring apparatuses with an increased degreeof freedom.

Next, the arrangement and operation of a fourth photometric apparatusaccording to the present invention will be described.

FIGS. 11 to 14 show embodiments of the fourth photometric apparatusaccording to the present invention.

First and second specific examples of the fourth photometric apparatusrelate to a photographic optical system and a photometric apparatus. Thefirst specific example is a photometric apparatus having at least onediffraction surface having an action by which an optical path is dividedin a photographic optical system, wherein at least a part of a bundle oflight rays passing through the diffraction surface is led to alight-receiving element for photometry. The photometric apparatus ischaracterized in that the diffraction surface has concentricrotationally symmetric patterns formed thereon. The second specificexample is a photometric apparatus in which at least one diffractionsurface having an optical path dividing action is provided on a lenssurface of a photographic optical system in an area where an effectiveray bundle passes, and is at least a part of a bundle of light rayspassing through the diffraction surface is led to a light-receivingelement for photometry. The photometric apparatus is characterized inthat the lens provided with the diffraction surface is disposed in thevicinity of a stop. Each of the first and second specific examples willbe described below.

[Eleventh Embodiment]

FIG. 11 is a conceptual view showing an eleventh embodiment of thepresent invention. A lens surface of a photographic optical system 1 isprovided with a diffraction surface 12 having concentric patterns whichare rotationally symmetric about the optical axis, as shown for examplein FIG. 13(a). The diffraction surface 12 has an action by which abundle of light rays passing through the diffraction surface 12 isdivided into a zero-order ray bundle 18 and a first-order ray bundle 19.A film plane 7 is placed at the image-formation position of thezero-order ray bundle 18 passing through the diffraction surface 12. Alight-receiving element 4 for photometry is placed at theimage-formation position of the first-order ray bundle 19 passingthrough the diffraction surface 12. In this embodiment, a part of thezero-order ray bundle 18 passing through the diffraction surface 12passes through a half-mirror 17 disposed behind the diffraction surface12 and is led to the film plane 7. On the other hand, a part of thefirst-order ray bundle 19 passing through the diffraction surface 12 isreflected by the half-mirror 17 and led to the light-receiving element 4to perform photometry.

In the eleventh embodiment, because the optical axes of the photographicand photometric systems are coincident with each other, there is noparallax between the photographic and photometric systems, and theaccuracy of photometry improves. Moreover, because the diffractionsurface 12 has concentric patterns which are rotationally symmetricabout the optical axis, the production of the diffraction surface 12 isfacilitated.

In the eleventh embodiment, the diffraction surface 12 having an opticalpath dividing action may be provided on only some portions of a lenssurface, as shown for example in FIG. 13(b). By doing so, the effect ofa diffraction surface manufacturing error on the image quality can bemade smaller than in a case where the entire area of a lens surface isformed as a diffraction surface.

[Twelfth Embodiment]

FIG. 12 is a conceptual view showing a twelfth embodiment of the presentinvention. A lens surface of a photographic optical system 1 is providedwith a diffraction surface 12 having concentric patterns whose center ofrotation is set off the optical axis, as shown for example in FIG.13(c), thereby deflecting the exit axis. In this embodiment, thediffraction surface 12 has been blazed for a specific wavelength and hasan exit axis deflecting action. In a bundle of light rays passingthrough the diffraction surface 12, light rays of specific wavelengthare bent and led to a light-receiving element 4 to perform photometry.The remaining light rays are led to the film plane 7 as they are to forman image thereon.

In the twelfth embodiment, it is possible to bend a ray bundle to anyimage-formation position at a specific wavelength. Accordingly, itbecomes possible to utilize even a small space present in a complicatedarrangement in a camera. Moreover, it becomes unnecessary to provide anoptical path bending member such as a half-mirror provided in theeleventh embodiment.

In the twelfth embodiment, the diffraction surface 12 may be provided ononly some portions of a lens surface. By doing so, the effect of adiffraction surface manufacturing error on the image quality can be madesmaller than in a case where the entire area of a lens surface is formedas a diffraction surface.

In either of the eleventh and twelfth embodiments, the diffractionsurface 12 having an optical path dividing action is disposed in thevicinity of a stop 16 in the photographic optical system 1. Many lightrays gather in the vicinity of the stop 16. Therefore, by providing thediffraction surface 12 in the vicinity of the stop 16, it becomespossible to efficiently capture a ray bundle over the entire area fromthe center to the periphery.

In the first and second specific examples of the fourth photometricapparatus according to the present invention, a DOE having a ray bundledividing action is provided in the optical path of the photographicoptical system, thereby eliminating a parallax between the photographicand photometric optical systems. Further, it becomes possible to performTTL metering in a lens shutter camera as well. Therefore, an improvementin the accuracy of photometry can be expected. Moreover, there is nophotometer window as is provided in the conventional apparatus.Accordingly, the design freedom increases. Furthermore, there is nolikelihood that a part of the acceptance angle will be vignetted by thelens barrel.

In the first specific example of the fourth photometric apparatus, theDOE is formed from concentric patterns. Thus, the production of the DOEis facilitated.

In the second specific example of the fourth photometric apparatus, itbecomes possible to efficiently capture a bundle of light rays. Thus,the accuracy of photometry can be improved.

A third specific example of the fourth photometric apparatus accordingto the present invention relates to a finder optical system and aphotometric apparatus. It is characterized in that at least onediffraction surface having an optical path dividing action is providedon a lens surface of a finder optical system in an area where aneffective ray bundle passes, and that at least a part of a bundle oflight rays passing through the diffraction surface is led to alight-receiving element for photometry.

The third specific example will be described below.

[Thirteenth Embodiment]

FIG. 14 is a conceptual view showing a thirteenth embodiment of thepresent invention. An objective lens surface of a finder optical system2 is provided with a diffraction surface 12 having an optical pathdividing action, such as that shown in FIG. 13(a) or 13(b). Zero-orderlight passing through the diffraction surface 12 is led to a finderfield system, whereas first-order light is reflected by a half-mirror17, which is disposed behind the objective lens, and led to alight-receiving element 4 to perform photometry.

In the above-described third specific example of the fourth photometricapparatus according to the present invention, there is no parallaxbetween the finder field system and the photometric system. Moreover,there is no photometer window as is provided in the conventionalapparatus. Accordingly, the design freedom increases. Thus, in thefourth photometric apparatus, a diffraction surface is given an exitangle deflecting action, thereby allowing the interior components of acamera to be arranged with an increased degree of freedom.

Next, the arrangement and operation of a fifth photometric apparatusaccording to the present invention will be described.

[Fourteenth Embodiment]

FIGS. 15, 16(a) and 16(b) show a fifth photometric apparatus accordingto the present invention. FIG. 15 is a conceptual view showing afourteenth embodiment of the present invention. A diffraction surface 12having a converging lens action is provided on a chamfered portion of anobjective lens 20 of a finder optical system 2, and a bundle of lightrays passing through the diffraction surface 12 is led to alight-receiving element 4. In the fourteenth embodiment, the photometricoptical system is completely independent of a bundle of light rays otherthan the ray bundle used for photometry. Therefore, the components canbe integrated into one unit without a possibility that a deteriorationof the performance due to a diffraction surface manufacturing error willaffect a ray bundle other than that used in the photometric opticalsystem. Thus, it becomes possible to reduce the size and cost of theapparatus.

As shown in the front view of FIG. 16(a) and the side view of FIG.16(b), the diffraction surface 12 may be provided on a collar portion ofany of lenses constituting the finder optical system 2. In this casealso, advantageous effects similar to those in the fourteenth embodimentare obtained.

It is also possible to provide the diffraction surface 12 on an externalportion of a photographic optical system or a distance measuring opticalsystem. In this case also, advantageous effects similar to those in thefourteenth embodiment are obtained.

In the above-described fifth photometric apparatus according to thepresent invention, the components of the photometric optical system andthose of another optical system can be integrated into one unit. Thus,it becomes possible to reduce the size and cost of the apparatus. Bygiving an exit angle deflecting action to the diffraction surface 12,the light-receiving element 14 can be disposed with a high degree offreedom. Thus, it becomes possible to make good use of the space in thecamera. It should be noted that it is preferable to provide alight-blocking member, e.g. a masking member, in the vicinity of theboundary between the two optical systems so that light rays in oneoptical system will not enter the other optical system.

Next, the arrangement and operation of a sixth photometric apparatusaccording to the present invention will be described.

FIGS. 17 and 18 show embodiments of a sixth photometric apparatusaccording to the present invention.

[Fifteenth Embodiment]

FIG. 17 is a conceptual view showing a fifteenth embodiment of thepresent invention, which has a distance measuring apparatus and aphotometric apparatus. One surface of a distance measuring opticalsystem 15 is provided with a diffraction surface formed in a multiplestructure consisting essentially of a diffraction surface 12 blazed forinfrared light and a diffraction surface 12′ having an exit angledeflecting action and blazed for visible light. A bundle of visiblelight rays is deflected by the diffraction surface 12′ and led to alight-receiving element 4 for photometry. A bundle of infrared lightrays passes through the diffraction surface 12 and is led to alight-receiving element 14 for distance measurement. In this embodiment,the photometric optical system and the distance measuring optical systemcan be integrated into one unit. Accordingly, the cost can be reduced bya reduction in the number of components, and the size of the apparatuscan be reduced by space savings.

[Sixteenth Embodiment]

FIG. 18 is a conceptual view showing a sixteenth embodiment of thepresent invention. Two diffraction surfaces 12 and 12′ having differentconverging lens actions are provided on the same substrate. One raybundle passing through the diffraction surface 12′ is led to alight-receiving element 14 for distance measurement, and another raybundle passing through the diffraction surface 12 is led to alight-receiving element 4 for photometry. The light-receiving elements 4and 14 are formed on the same chip. In this embodiment, the cost can bereduced by a reduction in the number of components. It is also possibleto simplify the assembly of the apparatus.

In the above-described sixth photometric apparatus according to thepresent invention, it is possible to reduce the cost and size of theapparatus by a reduction in the number of components. Further, by givingan exit angle deflecting action to the diffraction surface, the spacecan be effectively utilized, and thus a reduction in the size can beachieved. Moreover, it becomes possible to arrange the components withan increased degree of freedom. It is preferable to dispose alight-blocking member such that one ray bundle will not interfere withthe other ray bundle.

It should be noted that the sixth photometric apparatus is alsoapplicable to an active type light-projecting lens system and a passivetype photometric optical system. In such a use application also,advantageous effects similar to those stated above are obtained.

Next, the arrangement and operation of a seventh photometric apparatusaccording to the present invention will be described.

FIGS. 19 to 22 show embodiments of the seventh photometric apparatusaccording to the present invention.

[Seventeenth Embodiment]

FIG. 19(a) is a conceptual view showing a seventeenth embodiment of thepresent invention. In this embodiment, the present invention is appliedto a photometric apparatus for a lens shutter camera in which the angleof coverage is variable. As shown in FIG. 19(a), a DOE 10 hasdiffraction surfaces 12 and 12′ formed in parallel on the samesubstrate. The diffraction surfaces 12 and 12′ have different converginglens actions. The number of light-receiving elements 4 and 4′ which isequal to the number of diffraction surfaces provided are disposed atappropriate positions. A suitable light-receiving element is selectedaccording to photography conditions (e.g. a field angle change orswitching to the panoramic photography mode) to perform photometry.According to this embodiment, it is possible even with a lens shuttercamera to obtain the correct exposure at all times independently ofphotography conditions with a simple arrangement. In this embodiment,photometry can be effected even more accurately by selectively coveringan unnecessary area with a light-blocking member (e.g., a mask or aliquid-crystal shutter) 21.

[Eighteenth Embodiment]

FIG. 20 is a conceptual view showing an eighteenth embodiment of thepresent invention. A DOE 10 has diffraction surfaces 12 and 12′ formedin parallel on the same substrate. The diffraction surfaces 12 and 12′have different converging lens actions. A single light-receiving element4 is disposed behind the DOE 10. The DOE 10 slides vertically accordingto photography conditions (e.g. a field angle change or switching to thepanoramic photography mode), thereby selecting a necessary area toperform photometry. Moreover, in this embodiment, the thickness of thesubstrate varies for each of the diffraction surfaces 12 and 12′, sothat a bundle of light rays passing through either of the diffractionsurfaces 12 and 12′ forms an image at substantially the same position(i.e. the position of the light-receiving element 4). In thisembodiment, advantageous effects similar to those in the seventeenthembodiment are obtained.

Further, in this embodiment, the image-formation positions of raybundles passing through the diffraction surfaces 12 and 12′ can be madeapproximately coincident with each other by a combination of thethickness of the substrate and the converging actions of the diffractionsurfaces 12 and 12′. Thus, it is possible to reduce the number oflight-receiving elements to one. Even more accurate photometry can beperformed by covering an unnecessary area with a light-blocking member(e.g., a mask or a liquid-crystal shutter).

[Nineteenth Embodiment]

FIGS. 21(a) and 21(b) show different patterns for a DOE 10 used in aswitching type photometric apparatus similar to the above. In FIG.21(a), a plurality of diffraction surfaces having different converginglens actions are concentrically formed on the same substrate. In FIG.21(b), a plurality of diffraction surfaces having different converginglens actions are formed on the same substrate in a sectorial shape. Inthese cases, a light-receiving element 4 is disposed on an optical axisperpendicular to the pattern center a of the DOE 10, and an unnecessaryarea is covered with a light-blocking member (e.g. a mask) according tophotography conditions (e.g. a field angle change or switching to thepanoramic photography mode) to thereby select a necessary area. Thelight-receiving element 4 is moved along the optical axis according toeach particular image-formation position to perform photometry. In thisembodiment, advantageous effects similar to those in the seventeenthembodiment are obtained.

[Twentieth Embodiment]

FIG. 22 is a conceptual view showing a twentieth embodiment of thepresent invention. In this embodiment, the present invention is appliedto a photometric apparatus for a lens shutter camera in which the angleof coverage is variable, particularly for a camera having a zoom lens.The photometric apparatus includes DOEs 10 and 10′ provided withrespective diffraction surfaces 12 and 12′ having a converging ordiverging lens action. The spacing between the DOEs 10 and 10′ is variedaccording to photography conditions (e.g. a field angle change orswitching to the panoramic photography mode) to effect a magnificationchange, thereby performing photometry for each photography mode. In thisembodiment, advantageous effects similar to those in the seventeenthembodiments are obtained. In addition, it is possible to cope with acontinuous change in the field angle, and it becomes unnecessary to usea light-blocking member (e.g. a mask). The use of a DOE in avariable-magnification photometric optical system enables thephotometric mechanism to be formed in a relatively thin structure.

In the above-described seventh photometric apparatus according to thepresent invention, it is possible even with a lens shutter camera toobtain the correct exposure at all times independently of photographyconditions with a simple arrangement.

In the first to seventh photometric apparatuses according to the presentinvention, the diffraction surfaces may have a curvature. If adiffraction surface has a curvature, it is possible to share therefracting action at the diffraction surface and to increase the degreeof freedom of design for aberration correction. Thus, it is possible toattain a high-performance and highly optioned photometric apparatus. Inthe first to seventh photometric apparatuses, the diffraction surfacemay be a combination of a plurality of diffraction surfaces and lenscomponents. In this case, advantageous effects similar to those statedabove are obtained, and it is possible to attain a higher-performanceand even more highly optioned photometric apparatus.

The DOE may be arranged such that one surface thereof has a convergingpower, and the other surface thereof has a diverging power with thisarrangement, the position of the principal point of the DOE can bechanged, and thus the components of the photometric apparatus can bearranged with an increased degree of freedom. If the DOE is aplate-shaped DOE having flat surfaces on both sides thereof, it ispossible to further reduce the thickness, size and weight of theapparatus. The diffraction surface may be formed on a glass substrate.However, it is preferable to form a diffraction surface on a plasticsubstrate by molding. By doing so, it becomes possible to achieve ahigher level of mass-production and to further reduce the cost andweight of the apparatus.

As has been described above, according to the present invention, a DOEis provided in a photometric optical system of a camera, thereby makingit possible to provide a photometric apparatus for a camera whichsatisfies the demands for reductions in the size, thickness and cost ofthe apparatus. Further, the present invention enables the photometricapparatus to be highly optioned despite a simple arrangement whilesatisfying the demands for reductions in the size, thickness and cost.

What we claim is:
 1. A photometric apparatus for a camera, comprising: aplate-shaped photometer window on an outermost side, a photometricoptical system provided separately from a photographic optical system,and a light-receiving element for photometry, said photometric opticalsystem having at least one diffractive optical element having at leastone diffraction surface, and said diffractive optical element having alens action, wherein: said diffractive optical clement has saiddiffraction surface on a front side thereof.
 2. A photometric apparatusfor a camera, comprising: a plate-shaped photometer window on anoutermost side, a photometric optical system provided separately from aphotographic optical system, and a light-receiving element forphotometry, said photometric optical system consisting of onediffractive optical element having at least one diffraction surface, andsaid diffractive optical element having a lens action, wherein: saiddiffractive optical element has said diffraction surface on a front sidethereof.
 3. A photometric apparatus according to claim 1, wherein saiddiffractive optical element and said light-receiving element forphotometry are integral with each other.
 4. A photometric apparatusaccording to claim 1, wherein a bundle of light rays is deflected bysaid diffractive optical element.
 5. A photometric apparatus accordingto claim 1, wherein said diffraction surface has a curvature.
 6. Aphotometric apparatus according to claim 1, wherein said diffractiveoptical element comprises a plastic substrate.